A support tool in vertical heat treatment apparatus has been configured to have a vertical pair of endplates, and, for example, three struts being vertically arranged to be spanned between the two endplates, and a number of holding grooves being disposed in a longitudinal direction of the three struts at a constant interval and ditched to be opened facing one another, wherein a substrate is inserted between the holding grooves of the three struts, thereby a plurality of substrates are held in a horizontal position and in a line in a vertical direction with centers of them being aligned. However, in the support tool having such a configuration, since total weight of the substrates is supported only by the holding grooves at three points, there has been a problem that when thermal stress is suddenly applied to a substrate, crystal defects (slip) may occur, or the substrate may be warped due to tensile stress or empty weight stress between contact surfaces of the substrate and the holding grooves.
As a method of solving such a problem, there is a method in which the support tool includes a support member to be contacted to the substrate, and a support strip for supporting the support member, and the support member includes a silicon plate-like member (hereinafter, referred to as plate-structural support tool) having an area smaller than that of a flat surface of the substrate and a thickness larger than that of the substrate, thereby the total weight of the substrate are dispersed to reduce the tensile stress or the empty weight stress, so that occurrence of slip is suppressed (refer to patent literature 1).
[Patent literature 1]
WO2004/030073 pamphlet.